The present invention relates generally to liquid crystal display devices of the active matrix type; and, more particularly, the invention relates to a liquid crystal display device having switching elements formed of semiconductor devices, such as thin-film transistors, having an improved on-screen display image quality which is obtained by correcting such characteristic dispersions as deviations of threshold voltage values of the switching elements and/or fluctuations of the threshold value of the thin-film transistors.
In recent years, active-matrix liquid crystal display devices which use thin-film transistors as its switching elements have been widely employed for use as monitor units in various types in image visualization equipment and/or information processing apparatus.
A typical liquid crystal display device of this type is arranged to include an active matrix substrate with a plurality of (multiple) switching elements (thin-film transistors) for pixel selection formed on an electrically insulating or dielectric substrate and a color filter substrate having thereon a common electrode and a color filter, which substrates are bonded together to define therebetween a thin gap or space in which a layer of liquid crystals is sealed, to thereby provide a liquid crystal panel with requisite driver circuitry assembled together.
In recent years, as visual display monitors have been increasing in screen size and precision, it is becoming more and more difficult to make uniform the characteristics of those thin-film transistors formed on an active-matrix substrate. Another serious problem associated with currently available liquid crystal display architectures is the presence of risks of destruction and characteristic degradation of thin-film transistors due to the effects of static electricity during the manufacture of the liquid crystal display devices.
One typical prior known approach to making the thin-film transistor threshold value even is to apply thermal processing to finally manufactured thin-film transistors. In addition, one prior art electrostatic remedy is to provide one or more xe2x80x9cspecialxe2x80x9d leads for electrostatic protection at selected portions of a substrate to be cut away when the intended liquid crystal panel is completed, the electrostatic protective leads being connected to associative leads of thin-film transistors.
Unfortunately, the conventional approaches suffer from limitations for making the thin-film transistor threshold value even during thermal processing in the manufacture of active-matrix substrates, which can result in the presence of a non-uniformity or unevenness in the characteristics of respective active-matrix substrates. Such a transistor characteristic deviation leads to the occurrence of undesired brightness irregularities due to variations in voltage potentials being applied to a layer of the liquid crystals.
It is therefore a primary object of the present invention to provide a new and improved liquid crystal display device which is capable of avoiding the problems now faced in the prior art and which is also capable of increasing the manufacturing yield and reliability thereof.
To attain the foregoing object, the present invention provides a liquid crystal display device which is specifically arranged so that a plurality of parallel elongate pixel signal electrode leads formed on an active-matrix substrate are subdivided into two groups of odd-numbered and even-numbered leads in the order of the layout sequence as counted from one side edge of such a substrate, a first common wiring line (electrostatic protective common lead) is provided for protection of the group of odd-numbered pixel signal electrode leads against externally attendant static electricity, a second common wiring line (electrostatic protective common lead) is provided for protection of the remaining group of even-numbered pixel signal electrode leads against static electricity, and the first electrostatic protective common lead and the odd-numbered pixel signal electrode lead group, on one hand, and the second electrostatic protective common lead and the even-numbered pixel signal electrode lead group, on the other hand, are connected together via two electrostatic protective elements (mutually inversely coupled nonlinear elements or alternatively a resistive element), respectively.
The first and second electrostatic protective common leads are provided such that they are electrically independent of each other on the active enable successful defect inspection and threshold value adjustment of respective thin-film transistors of pixel signal electrode leads connected to these electrostatic protective common leads, while, in the state wherein a color filter substrate has been bonded, causing them be electrically connected together via a conductive member (conductive paste or the like) for use in electrically connecting the active-matrix substrate and a common electrode of the color filter substrate.
In addition, a third electrostatic protective common lead is provided at a location outside of the first and second electrostatic protective common leads in such a manner that the first and second plus third electrostatic protective common leads are, electrically independent of one another on the active-matrix substrate while, in the state that the color filter substrate has been bonded, letting these leads be electrically connected together via a conductive member for electrical connection between the active-matrix substrate and the common electrode of the color filter substrate.
Some typical arrangements unique to the instant invention are as follows.
(1) A liquid crystal display device comprises:
a color filter substrate having a common electrode formed on a dielectric substrate and color filters of multiple colors;
an active-matrix substrate disposed as to oppose the color filter substrate with a specified gap or space defined therebetween in which a layer of liquid crystals is sealed, thereby constituting a liquid crystal panel, the active-matrix substrate including a plurality of scan electrode leads formed on a dielectric substrate, a plurality of image signal electrode leads formed to cross over or xe2x80x9cintersectxe2x80x9d the scan electrode leads, a plurality of thin-film transistors which are two-dimensionally laid out to form an effective display area by connection to the scan electrode leads and image signal electrode leads, pixel electrodes connected to respective ones of the pixel electrodes, an additive capacitive element connected to each of the pixel electrodes, a common electrode lead terminal for connection to the common electrode formed on the color filter substrate, scan electrode lead terminals which extend from the scan electrode leads and image signal electrode leads up to one side outside of the effective display area, along with image signal electrode lead terminals which extend to the other side neighboring upon this one side, and a dielectric protective film coated so as to cover at least the thin-film transistors;
driver circuitry, including a scan electrode driver circuit and image signal electrode drive circuit, for supplying the scan electrode lead terminals and image signal electrode lead terminals with more than one signal voltage for on-screen image display;
first and second electrostatic protective leads extending along (in parallel to) one side with the pixel signal electrode lead terminals formed thereat and being electrically connected to respective ones of the first and second electrically divided common electrode lead terminals as formed along one opposite side, with the effective display area lying therebetween; and
first and second electrostatic protective elements for respectively connecting between the first and second electrostatic protective leads on one hand and the oddnumbered and even-numbered ones of the image signal electrode leads on the other hand, wherein
the first and second common electrode lead terminals are electrically connected together via a conductive member for electrical connection relative to the common electrode formed on the color filter substrate in the state that the color filter substrate has been bonded.
(2) A liquid crystal display device comprises:
a color filter substrate having a common electrode formed in a dielectric substrate and color filters of multiple colors;
an active-matrix substrate disposed so as to oppose the color filter substrate with a specified gap or space defined therebetween in which a layer of liquid crystals is sealed, thereby constituting a liquid crystal panel, the active-matrix substrate including a plurality of scan electrode leads formed on a dielectric substrate, a plurality of image signal electrode leads formed to cross over or xe2x80x9cintersectxe2x80x9d the scan electrode leads, a plurality of thin-film transistors two-dimensionally laid out to form an effective display area by connection to the scan electrode leads and image signal electrode leads, pixel electrodes connected to respective ones of the pixel electrodes, an additive capacitive element connected to each of the pixel electrodes, a common electrode lead terminal for connection to the common electrode formed on the color filter substrate, scan electrode lead terminals extended from the scan electrode leads and image signal electrode leads up to one side outside of the effective display area along with image signal electrode lead terminals extended to the other side neighboring upon this one side, and a dielectric protective film coated so as to cover at least the thin-film transistors;
driver circuitry including a scan electrode driver circuit and image signal electrode driver circuit for supplying the scan electrode lead terminals and image signal electrode lead terminals with more than one signal voltage for on-screen image display;
first, second, and third electrostatic protective lead terminals electrically divided and extending in parallel to the one side in which the pixel signal electrode lead terminals are formed and being formed along the opposite side with the effective display area lying therebetween;
first and second electrostatic protective leads for electrical connection to respective ones of the first and second plus third common electrode lead terminals along with a third electrostatic protective lead placed at a location opposite to the effective display area with respect to the first and second electrostatic protective leads; and
first and second electrostatic protective elements for connection between the first and second electrostatic protective leads on one hand and the odd-numbered and even-numbered ones of the image signal electrode leads on the other hand, wherein
the first and second plus third common electrode lead terminals are electrically connected together via more than one conductive member for use in electrically connecting between it and the common electrode formed on the color filter substrate in the state that the color filter substrate has been bonded.
(3) Two nonlinear elements that are inverse-directionally connected to each other are used as said electrostatic protective elements for connection between the electrostatic protective leads and the image signal electrode leads in the above paragraph (1) or (2).
(4) A resistive element is used as said electrostatic protective element for connection between the electrostatic protective leads and the image signal electrode leads in (1) or (2).
With such an arrangement, according to this invention, it is possible to achieve the intended remedy for elimination of any possible destruction of the thin-film transistors otherwise occurring due to static electricity by the presence of the electrostatic protective leads, while at the same time enabling correction or rectification of possible variations of the threshold values of respective thin-film transistors constituting the pixels through application of an appropriate voltage thereto and also making it possible to attain successful execution of the required test procedure for inspection of unwanted electrical short-circuiting between the image signal electrode leads and the scan electrode leads along with other lead inspection procedures. This in turn makes it possible to increase the manufacturing yield of a liquid crystal display device, thus enabling provision of a high-quality liquid crystal display device.
It is noted that the present invention should not be limited only to the above-noted arrangements and those embodiments as will be described later in the description, but may be modifiable and alterable into a wide variety of forms without departing from the true spirit and scope of the invention.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.